Even before the Tiger had been tested, the Chelyabinsk Kirov Factory had been tasked to install the tipping parts of the A-19 122 mm gun-howitzer in the SU-152 superstructure. The job was simplified by the fact that the A-19 and the ML-20 had identical carriages. Their barrels constituted the main difference between them. Plans called for the 122-millimeter heavy SP gun prototype to be finished by May 10, 1943, but that was not done for a variety of reasons.
While design work was being done to install the A-19 122 mm gun in the SU-152, GAU and the People’s Commissariat of Arms initiated projects to develop an armor-piercing shell for the ML-20 152-millimeter gun-howitzer. This munition, which was developed by the summer of 1943, was assigned the designation BR-540. GAU Artillery Committee Chairman Khokhlov wrote GABTU about the introduction of the new munition in his letter of June 14, 1943:
Concerning the addition of the armor-piercing tracer shell to the SU-152 SP gun’s basic load, the Artillery Committee of the GAU of the Red Army considers it necessary to inform regimental commanders of the following:
1. The cylindrical section of the armor-piercing tracer shell hull bears the following marking in black paint: BR-540.
2. In addition to its marking, the armor-piercing tracer shell differs from the concrete-piercing howitzer shell in that it has a shorter warhead.
3. The armor-piercing tracer shell may only be fired using a special charge in a case bearing the marking: “Charge, special, BR V0 = 600 m/s.”
4. Firing the shell using a full variable charge is strictly prohibited.
5. If no special charge is available, the shell may be fired using a full normal charge of a new device minus one equilibrium bag (base + 7 equilibrium bags).
6. When firing the armor-piercing tracer shell, the scale inscribed on the left half of the ST-10’s field of view with the following inscriptions must be used for laying the gun:[1]
ДГ
ПУШ
ПЕРВ
7. Use only the panoramic sight when laying the gun for firing the long-range high-explosive fragmentation shell with reduced variable charge.{3}
However, deliveries of the DR-540 armor-piercing shells were delayed. The SU-152’s first engagements took place with the standard basic load; forces in the field did not get the armor-piercing shells until August 1943.
Meanwhile, production of SP guns continued as usual. Since the second quarter of 1943 ended with the SU-152 behind schedule, the SP gun production quota for the third quarter was adjusted. Instead of 75 vehicles, the July plan called for 80 SP guns, and the numbers increased to 84 SU-152’s per month in August and September. In addition, a contract between the Kirov Factory of the People’s Commissariat of the Tank Industry and the GAU’s Artillery Tractor and Self-Propelled Artillery Department reduced the price of each SU-152 to 250,000 rubles.
By July 10, 1943, only 10 of the 80 SU-152’s had been accepted. This time, however, the situation was under controclass="underline" according to the schedule of the People’s Commissariat of the Tank Industry, full-scale production of SP guns was planned for the second half of the month. By the 20th, 36 vehicles had been accepted, and the factory met its quota of 80 SU-152’s by the end of July. Some modifications had been made to the vehicles produced late in the month. The handrail on the rear of the superstructure was strengthened and given three brackets. The SP gun received another design change in conjunction with the KV-1S. The exhaust stacks were altered and given a short, armored shield. The SU-152 was produced in that form until the end of September 1943.
August was a relatively calm month for the Chelyabinsk Kirov Factory. SP guns were not produced in a lump but were spread evenly over the month—28 vehicles by the 10th, 36 by the 15th, and the 84 set by the quota were delivered by September 1. However, there were some mishaps that only became apparent after the SP guns had been delivered to troops in the field. Sharonov, the Kirov Factory’s military representative, accepted several dozen SU-152’s with defective mantlets. The recoil mechanism keyhole was incorrect, which made it impossible to use the key to open the valve for filling the recoil mechanisms with fluid. The defect was identified after the SP guns had been sent to the Moscow Self-Propelled Artillery Center. The flaw had to be corrected on site, using gas cutting equipment.
By August, a list of SU-152 design changes that needed to be made based on field operations had been drawn up. There was also a backlog of problems that had been pending since the winter of 1943. B. G. Vershinin, chief of the Red Army’s Main Armor Directorate, wrote the GAU’s Artillery Committee about one of them on August 3:
According to the February 6, 1943, decision of the State Commission that tested the SU-152 prototype, the Kirov Factory and Factory No. 172 were required to move the traversing mechanism housing to the right in order to correct problems that made things difficult for the driver.
Six months have passed since this decision was made, but neither the Kirov Factory nor Factory No. 172 has made the change.
Moreover, as is apparent from Kirov Factory letter No. 2883 of July 24, 1943, that addressed, in part, the ML-20S howitzer’s traversing mechanism, Factory No. 172 is behind schedule on completing the job, and the Kirov Factory and Factory No. 172 have not reached a joint decision regarding the needed design changes.
Since I believe the situation concerning correction of this flaw in the SU-152 is completely unacceptable, I hereby urge you to take the appropriate steps to modify the ML-20S howitzer traversing mechanism as needed and immediately produce a prototype of the mechanism.
I request that Kirov Factory Dir. Comrade Zaltsman contribute to improving the location of the gun traversing mechanism and modifying it and develop the appropriate measures for improving the driver’s operating conditions.{4}
However, the letter had no impact. The SU-152 continued to have ML-20S systems with the old traversing mechanism that pressed against the driver-mechanic’s right shoulder and back at certain angles for the entire time it was in production. The mechanism was never shifted to the right, although this was done when the IS-152 (ISU-152) SP gun was designed.
Some changes regarding the location of the ammunition were considered. In August 1943, the BR-540 armor-piercing shell was added to the SU-152’s basic load. USA GABTU Chief Eng. Col. N. N. Alymov demanded a 50/50 ratio of armor-piercing and high explosive rounds from the Chelyabinsk Kirov Factory. If the armor-piercing shell required a different storage rack design, it would have to be modified as quickly as possible. The modifications were not required, however, but the workmanship of the storage racks needed to be improved. There had been cases in which 4–6 shells could not be placed in the storage rack due to poor workmanship. Also, in the field it was common to increase the basic load to 25 rounds. The problem was solved by placing the additional five rounds under the gun; the shells and charges lay on the floor, held in place by wooden blocks. A proposal was made to manufacture regular racks for the additional ammunition, but this was never done.